During the lifetime of an oil or gas well different operations are performed in order to monitor the state of the well, to carry out measurements, to stimulate or treat the well, to replace various equipment or tools, or to carry out other necessary work. Different downhole equipment is then attached to a continuous tubing and run into and retrieved from the well.
When performing the above mentioned interventions in a well, many types of equipment are used: a coiled tubing, wire or possibly just a string (so-called “slick-line”). The various types of intervention equipment for wells have to be selected depending on the complexity of the task to be performed.
Coiled tubing is used during larger work and, in particular, when there is a need of performing circulation, as during stimulation of the well (chemical treatment or fracturing). The disadvantage is that the intervention type is very expensive as the use of a drilling rig is required.
Wires are used when there is no need of circulation, e.g. during measurements. Wires may also be provided with conductors for power supply and signal transmission. Often, wires are used for the intervention due to their large rupture strength and, thereby, may be used when the tool is relatively heavy. Because of the spaces between the wire components, the disadvantage of the wire is that a particular injector for grease (so-called “grease injector head”) must be used, by which grease under pressure is continuously injected to seal around the wire. Even if the grease provides relatively low friction and enables lowering of the tool by its own weight, this method requires large investments for equipment and materials.
In some cases, when the tool to be lowered is not too heavy, for example during sample collecting, a string may be used. When such a thin string is used, the grease injector head mentioned above may be replaced by more simple sealing means, for example a so-called stuffing box. The stuffing box comprises a tubular sleeve of rubber or the like. The cable is tightly enclosed by the tubular sleeve in an extent preventing discharges but simultaneously without making the friction between the string and the sleeve too large. This is an inexpensive method of well intervention.
However, a disadvantage of the previous stuffing box types is that the providing of such a sealing around the string may result in a too large friction. Another disadvantage is that such strings have a limited strength, and also a limited usability as power supply or signal transmission means are not included.
The continuous tubing is usually wound on a large spool, where the continuous tubing includes small diameter cylindrical tubing made of metal or composites which have a relatively thin cross sectional thickness. Such tubing (a cable or pipe) is typically more flexible and lighter than a conventional drill string. It is much faster to run into and out of a well bore than conventional joined straight pipe since there is no need to connect or disconnect short segments of a straight pipe.
A cable or pipe reel assembly usually includes a stand for supporting a spool on which the cable or pipe is stored, a drive system for rotating the reel and creating back-tension during operation of the reel, and a “level winding” system that guides the cable or pipe as it is being unwound from and wound onto the spool. The level winding system moves the cable or pipe laterally across the reel so that the cable or pipe is laid across the reel in a neat and organized fashion. The cable or pipe reel assembly must rotate the spool to feed the cable or pipe to and from the injector and well bore. The cable or pipe reel assembly must also tension the cable or pipe by always pulling against the injector during normal operation. The injector must pull against the tension to take the cable or pipe from the cable or pipe reel, and the reel must have sufficient pulling force and speed to keep up with the injector and maintain tension on the cable or pipe as the cable or pipe is being pulled out of the bore by the injector. The tension on the cable or pipe must always be maintained. The tension must also be sufficient to wind the cable or pipe properly on the spool and to keep the cable or pipe wound on the spool. Consequently, a cable or pipe reel assembly is subjected to substantial forces and loads.
There exist cable or pipe reel stands for receiving common and ordinary shipping spools for use as working reels. These cable or pipe reel assemblies require inserting a shaft through the center of the spool, and inserting a pair of driving knobs, mounted to a drive plate on the stand, into the side of the spool to provide the connection for the drive system. As a consequence, this type of reel stand has several problems. First, the reel stand either has to be separable into two halves so that the sides of the stand can be moved laterally away from each other, or has to have sides of the stand capable of being swung outwardly, in order to allow the shipping spool of cable or pipe to be loaded on the stand. Secondly, the spool has to be carefully aligned with the drive system on the stand. Spools wound with cable or pipe are very large and heavy, where the weight may vary from 10000 to 20000 kg on average. They are cumbersome and difficult to manoeuvre. Consequently, aligning a spool and the drive system on a rocking ship or in high winds is a difficult task.
Third, as previously mentioned, standard and ordinary shipping spools are not built to handle the substantial loads encountered by a typical working spool.
Such continuous cable or pipe has been used successfully in the oil and gas industry for many years. The development of new technology has expanded the role of coiled tubing in completion, workover, drilling and production applications. The vast majority of technology and applications have focused on metallic coiled tubing. Although uses for metallic coiled tubular have significantly increased in the past twenty years, limitations are experienced on occasion with metallic tubular, including tensile strength limitations due to string weight and corrosion susceptibility from inhospitable conditions.
Technology advancements in non-metallic, composite based cable and pipe products have facilitated solutions to many of the limitations encountered with metallic coiled tubular.
Composite tubing is commonly composed of a combined resinous-fibrous outer tube concentrically encompassing a plastic inner tube, with the inner tube substantially providing the desired strength and protective properties. When manufactured, the inner tube commonly becomes integrally fixed to the outer tube. As compared to steel tubular of identical size, composite tubular tends to have lower weight, superior burst properties, improved flow coefficients and increased fatigue resistance, while steel tends to exhibit more favorable collapse, compressive and tensile properties. Thus, in certain applications, composite tubular is a direct alternative to steel while in other applications composites are the highly preferred option.
However, the composite tubing is stiffer than conventional steel tubing and therefore also more difficult to handle and/or manipulate, store and transport, which gives rise to the need for a reel assembly which can support these types of continuous composite tubing.
GB 2.294.674 describes a device for handling a rod made from a resiliently flexible and compression-resistant composite material, where the device comprises a reel on which the rod is wound in an elastic state, means for retaining the rod pressed against the barrel of the reel and means for driving said reel in rotation. The retaining means has at least one roller whose axis is parallel to the axis of the reel and of width essentially equal to the width of the barrel and spring means for applying the roller against the rod wound on the barrel of the reel.